Sensitive immunoassays for type C viral proteins (p30, reverse transcriptase) will be used to further explore the antigenic relationships of groups of type C viruses isloated from different mammalian species. Similar procedures will be used to test for the presence of type C viral components in tissues of animals from which such viruses have not yet been isolated. Additional assays for other virion components will also be developed. Attempts to isolate new infectious type C viruses will be directed primarily toward primate tissues and cultured cell lines. In vitro cocultivation will be employed and new isolates characterized by virologic, immunologic and nucleic acid hybridization techniques.